This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 100 13 625.7, filed on Mar. 18, 2000, the entire disclosure of which is incorporated herein by reference.
The invention relates to a thread brake for weaving looms, particularly weft thread brakes for controlling the weft tension.
Thread brakes for textile yarns are well known in the art. Such brakes are for example used for controlling the weft thread tension in a weaving loom. Many different thread brake constructions are currently in use.
German patent publication DE 34 46 567 C1 shows a weft thread brake with a controllable braking action. The known brake according to said publication comprises two elastic elements forming lamella which face each other to form a weft thread passage or gap. Electromagnetic control means are provided for adjusting or controlling the position of at least one of the lamella or elastic element to thereby control the braking force that is applied to the weft thread passing through the passage between the lamella.
German patent publication DE 43 06 911 C1 discloses a weft thread brake that also uses lamella type elements for forming the thread passage. The position of at least one of the lamella is variable by a stepping motor which controls the pressure applied to one of the lamella by an eccentric cam mounted to the rotating shaft of the stepping motor.
Another weft thread brake is disclosed in German patent publication DE 43 06 911 C1 and German patent publication DE 43 23 748 C1 discloses an improvement of the weft thread brake disclosed in the first mentioned German patent publication DE 43 06 911 C1. The improvement resides in an arrangement of a thread tension sensor positioned down stream of the weft thread brake as viewed in the direction of the weft thread motion. The output signal of the sensor is used for controlling the brake force applied by the weft brake to the weft thread as a function of the weft thread tension in a closed loop control.
A multitude of other thread brakes have become known. For example European patent publication EP 0 475 892 A1 discloses a brake belt cooperating with a controllable brake body arranged relative to the brake belt so that the weft thread end passes through between the belt and the body. European patent publication EP 0 467 059 A1 discloses a so-called looping angle brake. Such brakes control the braking force by varying the looping angle of the weft thread around a brake element.
European patent publications EP 0 524 429 A1 and EP 0 597 239 A1 disclose weft thread brakes that do not use two elastic elements that bare against one another in a spring-elastic manner. In this conventional construction of a weft brake, the lamella or elastic elements have been replaced by one spring element cooperating with a counter bearing member of rotational symmetry. The counter bearing member has the shape of a cam that has a circumference with at least one sector having a reduced diameter. The counter bearing member is mounted on the rotational shaft of an electric stepping motor.
German patent publication DE 695 14 069 T2 discloses a device for positively modulating the brake force applied to the weft thread supplied by a weft thread supply mechanism in the form of a supply drum. A stepping motor carrying a thread motion control lever on its shaft is arranged downstream of the thread supply drum in such a way that the weft thread is deflected more or less as the control lever rotates with its shaft.
It is a disadvantage of known electrically controllable weft thread brakes that they all have a substantial structural size which is inconvenient for installation in a loom, particularly where a plurality of such weft brakes must be mounted in a space that is relatively small, for instance when a plurality of weft threads having different colors must be supplied to the weft insertion device of the loom. The supply of a plurality of weft threads having different colors requires the arrangement of a respective plurality of weft brakes which in turn require the positioning of thread guides for leading the peripherally outer yarns to the weft insertion point. Leading the weft yarns over or through these thread guides exposes these outer yarns to a higher tension load than the tension load to which yarns positioned in the center of the thread supply. Further, as the RPM of the main loom drive shaft is increased, it becomes additionally necessary that the thread brakes work extremely fast and permit nevertheless the maintaining of a substantially constant weft thread tension in which tension changes are negligibly small during the several weft insertion phases. These requirements cannot be satisfactorily met at all times by conventional weft thread brakes.
In view of the above it is the aim of the invention to achieve the following objects singly or in combination:
to construct a thread brake particularly a weft thread brake in such a manner that is compact, and capable of a rapid reaction with precision and reliability;
to construct a weft brake for a plurality of weft threads whereby the thread tension shall be individually controllable for each weft thread or group of weft threads so that all weft thread of a group will have the same tension regardless of the position of the individual weft thread on its way to the weft insertion; and
to construct the weft brake for a plurality of weft threads in such a way that a convenient weft presentation for the weft insertion into the loom shed is achieved.
The thread brake according to the invention is characterized by at least one pair of two flexible elements such as lamella having a leaf spring characteristic that face each other or bear against each other to form a thread gap for passing a thread through the gap wherein the gap width is controlled by at least one controller in the form of a linear motor having a stator and a linearly moving member such as an armature or a pneumatic piston which is positioned for operatively influencing at least one of the flexible elements for adjusting the thread gap width.
The drive of the thread brake or rather the control of the weft tension by the operation of the weft brake by a linear motor permits a very compact construction which is capable of a rapid reaction and precise operation.
In a preferred embodiment, the linear motor comprises at least one stator and at least one linearly moving member that is effective with its free end on at least one of the two lamella forming a pair. In a preferred embodiment, the linear motor is an electrical, linear stepping motor or linear servo motor. However, it is also possible to use, for example, a pneumatically driven linear motor which is quite feasible in an air jet weaving loom where a source of pneumatic pressure is readily available.
The linearly movable member of the linear motor is effective with its free end on the lamella or at least one lamella of a pair of such lamella either directly or through an adjustment pin. Whether or not an adjustment pin is provided between the free end of the linearly movable member and the respective lamella depends on the structural requirements of the individual loom, particularly how the linear motor is to be arranged relative to the lamella.
If a loom uses a plurality of weft threads, for example of different colors, it is necessary to arrange several weft thread brakes as a multi-weft brake, so that each weft thread has its own brake. According to the invention the multi-thread brake preferably has a single fixed stator which cooperates with a plurality of linearly moveable members such as armatures, one of which is provided for each weft thread. In a multi-weft or multi-thread brake according to the invention, the individual armatures are arranged either along a linear row or along a curved path next to one another.
Preferably, the control of the linear motor, more specifically the control of the individual motion of the linearly moveable members of the linear motor, is derived directly from the central loom control. In a multi-weft brake, each linearly moveable member is individually controllable even though the multi-brake has only one stator.